This is one of the largest families of bees and is represented by about an equal number of spe-
cies in each of the six zoogeographic regions. It is morphologically the most uniform and discrete
familial assemblage within the Apoidea. While many of the characteristics of this family are
shared with other families of bees and to a lesser extent with the Sphecoidea, the Megachilidae
also possess many characteristics in common with the Scolioidea.

The family is composed of three subfamilies, the Fideliinae and Lithurginae which are all pol-
len-collecting bees, and the Megachilinae which are predominantly pollen-collecting species, but
which contain several genera that are cleptoparasitic mainly in the nests of other megachilids.
The Fideliinae are found only in Chile and South Africa, but both of the other subfamilies are
nearly cosmopolitan and are well represented in America north of Mexico. Most of the pol-
len-collecting species do not make their own burrows, but appropriate a wide variety of
pre-existing burrows, holes, shells and other cavities or construct their nests either in the open

attaching them to branches and so forth, or place them under stones, cow chips and so on. As a
consequence of these habits, many species readily accept artificial nesting devices, and this has
not only permitted detailed studies of their biology, but has also made possible the manipulation
and management of several species for use in the pollination of agricultural crops. However,
some species in certain genera (e.g., Megachile) and even some groups of species (e.g.,
Heteranthidium and Trachusa) do construct their own burrows. All of the pollen-collecting
Megachilidae use foreign materials in the construction of the cell walls. These materials include
leaves, plant down, leaf pulp, petals, resin, pebbles, mud, clay, and the like. The larvae spin tough
cocoons before pupation.

Apart from the cleptoparasitic species, many of the megachilids are highly restricted in their
intrafloral relationships and thus oligolecty is a relatively common phenomenon in this family.

This is a large group of mostly pollen-collecting species which are present on all the continents
and many of the islands. The subfamily is composed of two tribes, the Anthidiini and the
Megachilini, both of which are well represented by numerous species in America north of Mex-
ico.

Tribe ANTHIDIINI

Although this tribe is present throughout much of the world, it contains fewer species than
the Megachilini and, unlike that tribe, is represented by only a single species in Australia. Like
the Megachilini the pollen-collecting species use a wide variety of foreign materials in construct-
ing their nest cells, but are not known to use mud. While the majority of the Anthidiini are soli-
tary, some of the pollen-collecting species in certain genera (e. g., Heteranthidiian and
Trachusa) live in colonies.

Anthidium utahense Swenk
B. C, Mont, and Utah, south to Calif., Nev. and Ariz. Ecology: Nests in
ground in holes and crevices frequently using cavities made by other insects and
animals as well as artificial nest cavities which offer vertical holes at ground level.
Parasite: Dioxys productus (Cress.)? Pollen: Polylectic, stores pollen o{ Phacelia and

Insofar as known the species of this genus are cleptoparasites, chiefly in the nests of pol-
len-collecting bees of the tribe Megachilini (Ashnieadiella, Chalicodoma, Heriades, Hoplitis,
Osmia, Proteriades and Robertsonella). However, one of our species has been reared from a
nest of the genus Anthidium and some extralimital species o{ Stelis have been shown to be clep-
toparasites in the nests oi Ceratina and Euglossa.

The tribe Megachilini, which contains the well known leaf-cutter and mason bees, is
represented by numerous species throughout much of the world. Although some of these bees
are cleptoparasites, mainly in the nests of other Megachilini, most members of this tribe are pol-
len-collecting bees, and like the Anthidiini make use of a wide variety of foreign materials for
the construction of the cells in their nests. However, unlike the Anthidiini some of these bees
utilize mud for cell construction, but none is known to use plant down for this purpose. Some of
the species live in colonies (e.g., certain Chalicodoma and Osmia) which are communal and even
possibly quasisocial, but the majority of the species are solitary. Most of the species appropriate
a wide variety of pre-existing holes and cavities of all sorts in which to make their nests, but
some of them do excavate their own tunnels in the ground. In some classifications the tribe
Megachilini is divided into two subtribes, the Osmiini (arolium present) and the Megachilini
(arolium absent).

The bees of this genus nest in small holes, such as those made by emerging beetles in old logs,
dead branches, and pine cones. Insofar as known, the species are polylectic and have rather long
seasons of flight.

The bees of this genus appear to collect pollen almost exclusively from flowers of the
boraginaceous genus Cryptantha. Some of the species make their nests in the ground while
others construct them in preexisting holes in wood above ground.

This rather large genus of chiefly Holarctic bees occurs in Eurasia, Africa and in western
North America, west of the Great Plains. Although there is some evidence which indicates that
Ayithocopa should be merged with Hoplitis, these taxa are maintained as distinct in this catalog.

This genus, which is nearly cosmopolitan in distribution, has until recently included all of the
so-called leaf-cutter bees regardless of whether the various species cut leaves with which to
make their nests or not. As currently restricted, those species which make their nests with
pieces of leaves or petals belong to the genus Megachile while those which use resin, mud, or
other such material have been assigned to Chalicodoma Lepeletier and Creightonella Cockerell.
The latter genus does not occur in the Western Hemisphere. Some authors have concluded that
Chelostomoides Robertson warrants generic rank rather than subgeneric status within the

Euphorbia albomarginata, Heliotropium curassavicum var. oculatum, Lotus
comiculatus, Medicago sativa, Melilotus alba, Phacelia ramosissima, Polygonum
aubertii, Senecio douglasii, Solidago, Veronica. The name adopted by the International
Bee Research Association for this species is Megachile pacifica (Panzer); however, an
application pending before the International Commission on Zoological Nomenclature
requests that the Commission use its plenary powers to set aside all type selections for
Apis rotundata Fabricius, 1793, and to rule that the species is to be interpreted by
reference to a newly established neotype specimen. Thus, if the Commission rules
affirmatively on this application, the correct name for this species will be Megachile
rotundata (Fabricius) which is currently considered to be a synonym of Megachile

The bees of this subgenus appear to be specialists of the Onagraceae, collecting pollen espe-
cially from the large flowered species of the genus Oenothera. Apparently the species also
differ in that some excavate their own nesting burrows while at least one species appropriates
preexisting tunnels of other bees.